Naughty satellites provided a gift for physicists

Naughty satellites provided a gift for physicists

The elliptical orbits of the Galileo satellites 5 and 6 allowed the researchers to measure the gravitational time dilation with unprecedented accuracy. Relativistic eccentricity reaches a peak amplitude of approximately 370 nanoseconds, due to the shift in the height of the satellites

The unsuccessful launch of two global positioning satellites 4 years ago turned out to be a real gift for physicists. Scientists used the spacecraft 5 and 6 of the Galileo system to more accurately measure the gravitational time dilation.

Gravitational time dilation (gravitational redshift) is a key prediction of the general theory of relativity, which Albert Einstein published 100 years ago. Gravitational fields slow down the passage of time. The closer the watch is to a massive object, the slower the arrows will move for the external observer.

Time slowdown also occurs due to movement, as predicted by Einstein’s 1905 special theory of relativity. The faster you move, the slower the clock ticks (for the outside observer). Time dilation is not only a theoretical phenomenon. The satellites were supposed to use it to provide accurate readings to users on Earth. The researchers were able to measure the phenomenon in the field. The most famous case was recorded in 1976 using the Gravity Probe-A experiment. Then an atomic clock was sent to an altitude of 10,000 km, after which they compared the data with readings on Earth. The results confirmed the predictions of the general theory of relativity with an accuracy of 0.007%.

The measurements of the Gravity Probe-A were considered the gold standard for 40 years, until the Galileo 5 and 6 satellites appeared. The pair were launched on the Soyuz rocket in 2014 to join the European satellite navigation network. But things did not go according to plan. The bottom line is that the rocket launched satellites into irregular orbits (too elliptical for navigation). Both satellites rise and fall to 8,500 km in orbit twice a day.

This behavior is not suitable for navigation work and team members are still trying to figure out how to return satellites to a constellation. But this situation is ideal for changing the time dilation, especially since Galileo 5 and 6 have their own atomic clocks, which will remain stable for 3 million years.

Naughty satellites provided a gift for physicists

Due to a malfunction, the Galileo 5 and 6 satellites were launched into the wrong orbits during the launch on the Soyuz rocket in 2014. Subsequent maneuvers helped deploy their orbits, but the flight paths remain too elliptical to join the constellation.

New measurements have improved the accuracy of determining the gravitational deceleration time by 5 times compared with the indicators Gravity Probe-A. I am glad that the theory is confirmed by practical observations.

Extraordinary results were possible due to the unique characteristics of the Galileo satellites. It is necessary to thank for the stability of their onboard atomic clocks, accuracy in orbit, as well as the presence of laser reflectors, which provide the performance characteristics of independent and accurate measurements of the orbit from the Earth.

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